MRI and functional MRI (fMRI)

Magnetic Resonance Imaging (MRI) was first demonstrated in 1973, so it is older than the PET scan technique. Its usefulness to psychologists really blossomed in the 1990s with the development of a variation called functional MRI.

What is MRI? What is the big advantage of MRI? What was the big problem with it initially?

In MRI, a powerful magnetic field is placed around the brain. It temporarily holds the nuclei of the brain's atoms in one direction. When released, the atoms "wobble" back to their original positions and emit a weak radio frequency signal that can be picked up by a sensitive receiving device.

The big advantage of MRI in general is its noninvasive character. Unlike the PET scan, the MRI requires no substance to be put into the body. The big problem with MRI when first invented was that the image took several minutes to form, so patients had to hold still. Sometimes it was difficult to get a good image from children or severely ill people who could not keep still.

The imaging time problem was eliminated by a discovery by Sir Peter Mansfield at the University of Nottingham in 1980 of a technique 10,000 times faster than the original MRI. This led to a process called fast MRI (or echo-planar imaging, EPI). It was followed by an even faster form of MRI called functional MRI, or fMRI .

What are advantages of functional MRI? Why did one researcher call it a "wonder technique"?

By the early 1990s, fMRI was causing much excitement among researchers. One called it "the wonder technique we've all been waiting for" (Blakeslee, 1993). The researchers were excited because functional MRI (fMRI) costs about a fifth as much PET scans, produces sharper pictures, and is less dangerous for the person scanned. Unlike PET, which shows broad areas of activity, functional MRI is capable of showing activity in areas a few millimeters across, as small as a BB.

With all its advantages, fMRI has been a boon to cognitive neuroscience researchers. Unless otherwise stated, it is the technique used to document areas of the brain activated by different mental activities, in chapters ahead.

A variety of other brain scanning techniques exist. MEG (magnetoencephalography) directly detects weak magnetic fields in small patches of nerve cells. As of 2002, it is still prohibitively expensive for most researchers. Other techniques like R-TOI (Real-Time Optical Imaging) provide additional ways to measure brain activity, while diffusion tensor imaging (DTI) is the method of choice for visualizing white matter in the brain.


Write to Dr. Dewey at psywww@gmail.com.

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